CPIEMICAI, TESTS AND ANALYSES 261 



For practical factory tests of fresh milk on the receiving plat- 

 form, determining its fitness for condensing, the reader is referred 

 to Chapter III, "Inspection of Milk at the Condensery," pp. 44 to 49. 



Milk 



SPECIFIC GRAVITY 



AEROMETRIC METHOD BY MEANS OF THE QUEVENNE LACTOM- 

 ETER. Use an accurate Quevenne lactometer with thermometer at- 

 tachment and a lactometer cylinder about ten inches high and one 

 and one-half inches wide. Fill the cylinder with milk at a tem- 

 perature between 5.5 and 65 degrees F. Insert the lactometer and 

 when it has found its equilibrium, note the point on the scale at the 

 surface of the milk. The correct temperature is 60 degrees F. For 

 every degree Fahrenheit above 60 add one-tenth point to the ob- 

 served reading, and for every degree Fahrenheit below 60 deduct 

 one-tenth point from the observed reading. This rule holds good only 

 when the range of temperature is within the limits of 55 degrees 

 and 65 degrees F. 



The specific gravity is calculated by adding 1,000 to the lactom- 

 eter reading and dividing the sum by 1,000. Example: Lactometer 

 reading is 31 at 65 degrees F. Corrected reading is 31.5; 



31.5 + 1000 

 specific gravity is - 



GRAVIMETRIC DETERMINATION. This consists of the filling of 

 a perfectly dry picnometer or other graduated flask of known meas- 

 ure with milk at the standard temperature (60 degrees F., or 15.5 

 degrees C.) and weighing the flask and contents. The weight of 

 the flask is then deducted from the weight of the flask plus con- 

 tents and the difference is divided by the weight of an equal volume 

 of water at standard temperature. The result is the specific gravity 

 of the milk. 



The Westphal balance method furnishes another accurate means 

 of determining the specific gravity. Both the gravimetric method 

 and the Westphal balance method, while accurate when operated 

 by the skillful chemist, require considerable time. Experimental 

 comparisons have demonstrated that for all practical purposes the 

 Quevenne hydrometer, when accurately graduated, yields correct 

 results, and the simplicity and rapidity of its operation render its 



